The invention relates to a continuously variable transmission and to a working machine comprising such a continuously variable transmission.
The invention is applicable on working machines within the fields of industrial construction machines, in particular wheel loaders, graders and articulated haulers. Although the invention will be described hereinafter with respect to a wheel loader, the invention is not restricted to this particular machine, but may also be used in other heavy working machines, such as dump trucks, excavators or other construction equipments.
A continuously variable transmission is a transmission which speed ratio can be continuously varied over a designed range. Continuously variable transmissions are useful due to enabling operation of a prime mover at optimum speed or at optimum fuel economy while still providing a desired rotational speed at the output shaft of the transmission. In a continuously variable transmission a speed ratio between the output shaft speed to the input shaft speed of zero may be obtainable. Such a continuously variable transmission is usually referred to as an infinitely variable transmission. The existence of an output to input speed ratio of zero enables a geared neutral function where the input shaft is rotating when the output shaft stands still. The presence of a geared neutral position is useful in many industrial contexts, such as within gearboxes of working machines for example, since it may obviate the need of a starting clutch or a torque converter. Furthermore, infinitely variable transmissions facilitate separation of operation of a hydraulic system included for performing lifting operations and/or steering the working machine from the propulsion of the working machine, since the hydraulic system can be powered from a power take off at an input shaft, which may be kept running, while an output shaft connected to propulsion drive train can be kept at stand still. A typical arrangement of a continuously variable transmission includes a continuously variable unit, variator unit, having a variator input shaft and a variator output shaft connected to a planetary gear system.
An example of a continuously variable transmission is disclosed in U.S. Pat. No. 7,220,203. The continuously variable transmission in U.S. Pat. No. 7,220,203 comprises a battery coupled to two motor/generators, respectively.
Accordingly, the continuously variable transmission in U.S. Pat. No. 7,220,203 is an electrically continuously variable transmission. Moreover, the electrically continuously variable transmission includes an input member to receive power from an engine and an output member for transmitting torque to e.g. the wheels of a working machine. Also, the electrically continuously variable transmission comprises planetary gear sets and a plurality of clutches. An advantage with the electrically continuously variable transmission disclosed in U.S. Pat. No. 7,220,201 is that the plurality of clutches allows additional fixed speed ratios and an additional compound-power-split speed ratio range in relation to the prior art known to U.S. Pat. No. 7,120,203.
However, the continuously variable transmission disclosed in U.S. Pat. No. 7,220,203 is in need of further improvements in terms of e.g. reduced costs in terms of reduced number of components, as well as optimizing the utilization of the variator unit.
It is desirable to provide a continuously variable transmission having improved functionalities in relation to prior art solutions.
According to a first aspect of the present invention there is provided a continuously variable transmission, comprising a variator unit having a variator input shaft and a variator output shaft; a first planetary gear set having a first, a second and a third planetary member, the first planetary member being one of a ring wheel and a planet carrier, the second planetary member being the other one of the ring wheel and the planet carrier, and the third planetary member being a sun wheel, wherein the first planetary member of the first planetary gear set is operatively connected to a transmission input shaft; and a second planetary gear set having a sun wheel, a ring wheel and a planet carrier, the planet carrier being operatively connected to a transmission output shaft; wherein the variator input shaft is operatively connected to the second planetary member of the first planetary gear set; the variator output shaft is operatively connected to the sun wheel of the first planetary gear set, the sun wheel of the first planetary gear set being further operatively connected to the sun wheel of the second planetary gear set while having a variable gear ratio between the transmission input shaft and the transmission output shaft; and the ring wheel of the second planetary gear set being selectively connectable to the second planetary member of the first planetary gear set and to a gearbox housing of the continuously variable transmission.
The wording “selectively connectable” should in the following and throughout the entire description be interpreted as two or more components being arranged to be actively connected/disconnected to each other. When discussing “selectively connectable” by means of components in a planetary gear set, the connection between e.g. a sun wheel and a ring wheel via the planet wheels of a planet carrier should not be construed such as the sun wheel being connected to the ring wheel unless otherwise described, which will be discussed further below. Accordingly, in order for a component of a planetary gear set to be connected to another component of the same planetary gear set, the two components must, in order to be connectable to each other in accordance with the intended interpretation of the wording in the present application, be locked to each other in some way or another.
An advantage of the present invention is that the variator output shaft is connected to the sun wheel of the first planetary gear set and the sun wheel of the second planetary gear set, thereby providing a desired maximum speed of the variator output shaft, while having a variable gear ratio between the transmission input shaft and the transmission output shaft. Also, the continuously variable transmission comprises fewer components in relation to prior art solutions, or more specifically, the present invention is not in need of all the clutches described in the prior art.
According to an example embodiment, a first clutch unit may be arranged between the second planetary member of the first planetary gear set and the ring wheel of the second planetary gear set, and a second clutch unit may be arranged between the ring wheel of the second planetary gear set and the gearbox housing.
Hereby, the first clutch unit may be arranged to controllably connect the second planetary member of the first planetary gear set to the ring wheel of the second planetary gear set. Further, the ring wheel of the second planetary gear set is then also connected to the variator input shaft.
Moreover, the second clutch unit hence allows for connection between the ring wheel of the second planetary gear set to the gearbox housing of the continuously variable transmission, i.e. the ring wheel of the second planetary gear set can, by means of the second clutch unit, be locked to the gearbox housing of the continuously variable transmission.
By means of the first clutch unit and the second clutch unit, a first and a second operating mode of the continuously variable transmission is enabled. In the event the ring wheel of the second planetary gear set is connected to the gearbox housing, the continuously variable transmission will be worked in the first operating mode where the second planetary gear set will work as a reduction gear set enabling a large transmission ratio over the second planetary gear set. In the event the ring wheel of the second planetary gear set is connected to the second member of the first planetary gear set, the continuously variable transmission will be worked in the second operating mode, where the first and second planetary gear sets will work as a bridge, where the variator input shaft and the variator output shaft are neither connected to the transmission input shaft nor the transmission output shaft. Hence, in the first operating mode the second planetary gear set works as a reduction gear set and in the second operating mode the second planetary gear set merges power supplied to its sun wheel and ring wheel. Accordingly, a mode selection arrangement may be provided which enables different operating modes with different bands of continuously variable speed ratios between the transmission input shaft and the transmission output shaft.
Moreover, the mode selection arrangement may, in addition to the clutch units, comprise a set of actuators. The actuators may control the engagement and disengagement of the clutch units. Still further, the mode selection arrangement may include a control unit or the like for operating the actuators.
According to an example embodiment, the first clutch unit and/or the second clutch unit may be a friction disc clutch unit.
A friction disc clutch unit is well known and easy to control. Also, the friction disc clutch unit has the advantage of being able to slip into engagement, providing a relatively even and smooth transition from a disengaged state to an engaged state, or vice versa. The friction disc clutch unit may be either a wet friction disc clutch unit or a dry friction disc clutch unit. However, other types of clutches are of course also conceivable, such as e.g. a dog clutch.
According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the variator input shaft, and a gear wheel connected to the second planetary member of the first planetary gear set, the gear wheels are in meshed connection with each other. The gear wheel connected to the second planetary member of the first planetary gear set may be further selectively connectable to the ring wheel of the second planetary gear set.
An advantage is that, by means of these gear wheels, the maximum speed of the variator input shaft may be adapted to various types of machines used in the variator unit.
According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the sun wheel of the first planetary gear set, and a gear wheel connected to the sun wheel of the second planetary gear set; the gear wheels are in meshed connection with each other. The gear wheel connected to the sun wheel of the first planetary gear set may be further connected to the variator output shaft.
According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the second planetary member of the first planetary gear set, and a gear wheel selectively connectable to the ring wheel of the second planetary gear set, wherein the gear wheels are in meshed connection with each other.
By arranging a gear wheel connected to the sun wheel of the first planetary gear set which is in meshed connection with a gear wheel connected to the sun wheel of the second planetary gear set, in combination with arranging a gear wheel connected to the second planetary member of the first planetary gear set which is in meshed connection with a gear wheel selectively connectable to the ring wheel of the second planetary gear set, a difference in geometric level between the first and the second planetary gear sets is provided. Hereby, the prime mover of a working machine can be positioned at a higher geometric level in comparison to the wheels of the working machine. Also, the freedom of choosing basic speed ratios of the first and the second planetary gear sets may be increased by adjusting the gear ratios of the two gear stages obtained by the mentioned gear wheels.
According to an example, the gear wheel selectively connectable to the ring wheel of the second planetary gear et may be further connected to the variator input shaft. According to another example, the gear wheel connected to the second member of the first planetary gear set may be further connected to the variator input shaft.
According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the sun wheel of the first planetary gear set, and a gear wheel connected to the variator output shaft; the gear wheels are in meshed connection with each other. The gear wheel connected to the variator output shaft may be further connected to the sun wheel of the second planetary gear set.
According to an example embodiment, the continuously variable transmission may further comprise a gear wheel connected to the ring wheel of the second planetary gear set, and a gear wheel selectively connectable to the variator input shaft; the gear wheels are in meshed connection with each other. The gear wheel selectively connectable to the variator input shaft may be further selectively connectable to the gearbox housing of the continuously variable transmission.
Hereby, a further difference in geometric level between the first and the second planetary gear sets is provided.
According to an example embodiment, one of the sun wheel, the ring wheel and the planet carrier of the second planetary gear set may be selectively connectable to another one of the sun wheel, the ring wheel and the planet carrier of the second planetary gear set.
Hereby, the continuously variable transmission enables for a third operating mode by simply selectively connecting one of the components of the second planetary gear set to another one of the components of the second planetary gear set. In this third operating mode, the second planetary gear set is by-passed or locked together as a direct gear without any increase/decrease in gear ratio, i.e. a 1:1 relationship of input to output of the second planetary gear set. By use of the third operating mode, the continuously variable transmission is provided with a mode which is faster than the second operating mode. Accordingly, the three operating modes are executed in its consecutive order when accelerating the vehicle, i.e. first the continuously variable transmission is operated by the first operating mode, then by the second operating mode and finally by the third operating mode.
It should be readily appreciated that the wording “selectively connectable” should be interpreted such that one of the sun wheel, the ring wheel and the planet carrier is able to be locked to another one of the sun wheel, the ring wheel and the planet carrier. Accordingly, the two components being connected to each other do not have a relative speed difference between themselves.
Furthermore, the components, i.e. one of the sun wheel, the ring wheel and the planet carrier may be selectively connectable to another one of the sun wheel, the ring wheel and the planet carrier by means of e.g. a clutch unit or the like. The clutch unit may, for example, be a friction disc clutch unit or any other suitable clutch unit such as those described above in relation to the description of the first clutch unit and the second clutch unit.
According, to an example embodiment, the sun wheel of the second planetary gear set may be selectively connectable to the planet carrier of the second planetary gear set.
Hereby, a clutch unit may be positioned between the sun wheel and the planet carrier of the second planetary gear set. When connecting the sun wheel to the planet carrier, the second planetary gear set will be by-passed and hence un-loaded.
According to an example embodiment, the planet carrier of the second planetary gear set may be selectively connectable to the ring wheel of the second planetary gear set.
Hereby, a clutch unit may be positioned between the planet carrier and the ring wheel of the second planetary gear set.
According to an example embodiment, the sun wheel of the second planetary gear set may be selectively connectable to the ring wheel of the second planetary gear set.
Hereby, a clutch unit may be positioned between the sun wheel and the dug wheel of the second planetary gear set. The power to the sun wheel and the power to the ring wheel will be merged together and thereafter provided to the planet carrier.
Accordingly, an advantage is that by simply providing the additional clutch unit enables for the third operating mode for the continuously variable transmission.
According to an example embodiment, the continuously variable transmission may further comprise a gear wheel selectively connectable to the sun wheel of the first planetary gear set, and a gear wheel connected to the ring wheel of the second planetary gear set; the gear wheels are in meshed connection with each other. The gear wheel connected to the ring wheel of the second planetary gear set may be further selectively connectable to the second planetary member of the first planetary gear set and to the gearbox housing of the continuously variable transmission.
Hereby, a further set of gear wheels are arranged between the sun wheel and the ring wheel of the second planetary gear set. This further gear set, in combination with the gear set having a gear wheel connected to the sun wheel of the second planetary gear set and a gear wheel connected to the sun wheel of the first planetary gear set and to the variator output shaft, enables for a fixed ratio in rotational speed between the sun wheel of the second planetary gear set and the ring wheel of the second planetary gear set. Accordingly, a clutch unit or the like may be positioned between this further gear set and the variator output shaft. Hereby, the further set of gear wheels, in combination with the gear set having a gear wheel connected to the sun wheel of the second planetary gear set and a gear wheel connected to the sun wheel of the first planetary gear set and to the variator output shaft, makes it possible to choose gear ratio between the sun wheel of the second planetary gear set and the ring wheel of the second planetary gear set.
Accordingly the above described 1:1 relationship for the second planetary gear set may be adjusted such that another gear ratio is provided, or keeping the 1:1 relationship if desired. Hence, the flexibility of choosing gear ratio between input and output for the second planetary gear set is increased.
Hence, the above description that the connection between components of the second planetary gear set should be interpreted as a connection which does not allow for a relative motion between the connected components is not fully applicable to this example embodiment of the present invention, since, as described, a relative motion is possible by means of the intermediate gear wheels.
According to an example embodiment, the variator unit may have a first hydraulic machine provided with the variator input shaft and a second hydraulic machine provided with the variator output shaft, the first and second hydraulic machines being hydraulically connected to each other.
According to an example embodiment, the variator unit may have a first electric machine provided with the variator input shaft and a second electric machine provided with the variator output shaft, the first and second electric machines being electrically connected to each other.
According to a second aspect of the present invention there is provided a continuously variable transmission, comprising a variator unit having a variator input shaft and a variator output shaft; a first planetary gear set having a first, a second and a third planetary member, wherein the first planetary member of the first planetary gear set is operatively connected to a transmission input shaft; and a second planetary gear set having a first, a second and a third planetary member, the third planetary member of the second planetary gear set being operatively connected to a transmission output shaft; wherein the variator input shaft is operatively connected to the second planetary member of the first planetary gear set; the variator output shaft is operatively connected to the third planetary member of the first planetary gear set, the third planetary member of the first planetary gear set being further operatively connected to the first planetary member of the second planetary gear set; the second planetary member of the second planetary gear set being selectively connectable to the second planetary member of the first planetary gear set and to a gearbox housing of the continuously variable transmission, and wherein one of the first, the second and the third member of the second planetary gear set is selectively connectable to another one of the first, the second and the third member of the second planetary gear set.
Effects and features of this second aspect of the present invention are largely analogous to those described above in relation to the first aspect of the present invention.
According to an example embodiment, the first planetary member of the second planetary gear set may be selectively connectable to the second planetary member of the second planetary gear set.
According to an example embodiment, the first planetary member of the second planetary gear set may be selectively connectable to the third planetary member of the second planetary gear set.
According to an example embodiment, the second planetary member of the second planetary gear set may be selectively connectable to the third planetary member of the second planetary gear set.
According to an example embodiment, the first planetary member of the first planetary gear set may be one of a ring wheel and a planet carrier, the second planetary member of the first planetary gear set may be the other one of the ring wheel and the planet carrier, and the third planetary member may be a sun wheel.
According to an example embodiment, the first planetary member of the second planetary gear set may be a sun wheel, the second planetary member may be a ring wheel, and the third planetary member may be a planet carrier.
According to an example embodiment, the variator unit may have a first hydraulic machine provided with the variator input shaft and a second hydraulic machine provided with the variator output shaft, the first and second hydraulic machines being hydraulically connected to each other.
According to an example embodiment, the variator unit may have a first electric machine provided with the variator input shaft and a second electric machine provided with the variator output shaft, the first and second electric machines being electrically connected to each other.
According to a third aspect of the present invention, there is provided a working machine comprising one of the above described continuously variable transmissions in relation to the first and second aspect of the present invention.
Effects and features of this third aspect of the present invention are largely analogous to those described above in relation to the first and second aspects of the present invention.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention. For example, the above description of the different advantages of the present invention is only described in relation to driving the vehicle in a forward direction, the various embodiments of the invention are of course also applicable when providing the continuously variable transmission in reversed gear, i.e. when the working machine is driving backwards.